Emulsion-polymerized addition polymers are prepared by the polymerization of ethylenically-unsaturated monomers using ionic- or free radical-initiated and propagated reactions. In most cases these reactions will not proceed to the point of 100% conversion of the ethylenically-unsaturated monomer to polymer within a reasonable time. Elimination of the residual monomer may be desirable due to odor, instability, or toxicity, for example, resulting from the residual monomer. Subsequent elimination of the remaining ethylenically-unsaturated monomer by conversion to polymer by methods such as, for example, heating for prolonged periods, with or without the addition of an ion- or a free radical-source; or physical removal of residual ethylenically-unsaturated monomer by methods such as, for example, vacuum stripping and steam sparging; or conversion to a less undesirable species such as, for example, conversion to a non-volatile adduct have all been disclosed in the past. However, concerns about the toxicity or odor of organic compounds in general, and of ethylenically-unsaturated monomers in particular, have lowered the level of residual ethylenically-unsaturated monomer which is acceptable in emulsion-polymerized addition polymers, and coatings that contain them, to levels which are frequently difficult and costly to achieve by conventional techniques. One category of ethylenically-unsaturated monomers is carboxylester monomers wherein at least one carboxylester grouping, —COOR, is present. In addition, ethylenically-unsaturated monomers may contain, as an impurity, saturated organic carboxylesters, i.e., compounds bearing at least one ester grouping which compounds are not ethylenically-unsaturated, and which persist in the emulsion polymer latex. Further, polymerization adjuvants may introduce additional organic carboxylesters, i.e., compounds bearing at least one ester grouping but which may not be ethylenically-unsaturated monomers. Such compounds, too, may give rise to concerns about toxicity or odor and should be eliminated from low odor coating compositions and low odor paints.
In the case of polymers comprising polymerized units of vinyl acetate monomer, residual vinyl acetate is also a source of odor. Moreover, the slow in situ hydrolysis of vinyl acetate to vinyl alcohol and subsequent rearrangement to acetaldehyde is an additional concern from both an odor and toxicity standpoint.
U.S. Pat. No. 5,422,269, to Nicks et al., discloses a method for reducing the residual levels of monomeric ethylenically-unsaturated carboxylic acid esters, such as alkyl acrylates and alkyl methacrylates, in surfactant stabilized dispersions of polymer of these monomers, such as latices or products formulated from latices. The residual monomer content is reduced by treatment with a hydrolytic enzyme, particularly a lipase or esterase, which treatment reduces the odor arising from the presence of the monomers. However, this disclosure does not discuss properties of formulated coatings or paints and the methods described therein have failed to result in any commercially viable low odor paints because the enzymes described therein and the levels of use disclosed therein result in enzyme degradation of paints. That is, the enzyme is active in attacking esters present in useful paint formulation components.
U.S. Pat. No. 7,014,909, to Rozynov et al., discloses methods for scavenging aldehydes from printed materials, however, Rozynov does not disclose methods to remove vinyl acetate or the conversion of vinyl acetate to acetaldehyde, and, moreover, the methods disclosed therein are not effective in removing acetaldehyde, which is the more prevalent and worrisome residual aldehyde in vinyl acetate-acrylic emulsion polymer latexes.
It is, therefore, an object of this invention to provide stable aqueous polymer compositions and coatings compositions having low odor. It is an additional object of this invention to provide stable aqueous polymer compositions and coatings compositions having a headspace VOC level, as measured by headspace GC-MS at 33° C., of less than 10 ppm, and preferably less than 5 ppm, for both organic carboxylester and acetaldehyde. In one embodiment of the invention, it is a further object of the invention to provide such compositions having a headspace VOC level of less than 10 ppm, and preferably less than 5 ppm, for both organic carboxylester and acetaldehyde, and an ester hydrolysis enzyme activity of less than 0.030 micromole/minute. It is also an object of this invention to provide a method for producing stable aqueous polymer compositions and coatings compositions having low odor, and having a headspace VOC level of less than 10 ppm, and preferably less than 5 ppm, for both organic carboxylester and acetaldehyde.